Rails模型has_many與多個foreign_keys

Question

相對較新的軌道，並試圖用一個名稱，性別，father_id和mother_id（父母）的單人模型來建模一個非常簡單的家庭「樹」。下面基本上是我想要做的，但顯然我不能重複：has_many中的孩子（第一個被覆蓋）。

class Person < ActiveRecord::Base 
    belongs_to :father, :class_name => 'Person' 
    belongs_to :mother, :class_name => 'Person' 
    has_many :children, :class_name => 'Person', :foreign_key => 'mother_id' 
    has_many :children, :class_name => 'Person', :foreign_key => 'father_id' 
end 

是否有與2個外鍵使用的has_many，或者可能改變基於對象的性別外鍵的簡單方法？或者還有其他更好的方法嗎？

謝謝！

Answer 1

發現IRC上一個簡單的答案，似乎工作（感謝雷達）：

class Person < ActiveRecord::Base 
    belongs_to :father, :class_name => 'Person' 
    belongs_to :mother, :class_name => 'Person' 
    has_many :children_of_father, :class_name => 'Person', :foreign_key => 'father_id' 
    has_many :children_of_mother, :class_name => 'Person', :foreign_key => 'mother_id' 
    def children 
    children_of_mother + children_of_father 
    end 
end 

Answer 2

我相信你可以實現你想使用的關係：has_one。

class Person < ActiveRecord::Base 
    has_one :father, :class_name => 'Person', :foreign_key => 'father_id' 
    has_one :mother, :class_name => 'Person', :foreign_key => 'mother_id' 
    has_many :children, :class_name => 'Person' 
end 

我會在下班後確認並編輯此答案; ）

Answer 3

使用在Person模型named_scopes 做到這一點：

class Person < ActiveRecord::Base 

    def children 
     Person.with_parent(id) 
    end 

    named_scope :with_parent, lambda{ |pid| 

     { :conditions=>["father_id = ? or mother_id=?", pid, pid]} 
    } 
end 

Answer 4

我更喜歡使用範圍爲這個問題。就像這樣：

class Person < ActiveRecord::Base 
    belongs_to :father, :class_name => 'Person' 
    belongs_to :mother, :class_name => 'Person' 
    has_many :children_of_father, :class_name => 'Person', :foreign_key => 'father_id' 
    has_many :children_of_mother, :class_name => 'Person', :foreign_key => 'mother_id' 

    scope :children_for, lambda {|father_id, mother_id| where('father_id = ? AND mother_id = ?', father_id, mother_id) } 
end 

這招可以很容易地讓孩子們在不使用實例：

Person.children_for father_id, mother_id 

Answer 5

爲了改善Kenzie的回答，您可以實現一個ActiveRecord關係定義Person#children，如：

def children 
    children_of_mother.merge(children_of_father) 
end 

看到this answer更多細節

Answer 6

不是解決所述的一般問題（「有多個外鍵的has_many」），但是，鑑於一個人既可以是母親也可以是父親，但不是兩者，我將添加gender列並使用

has_many :children_of_father, :class_name => 'Person', :foreign_key => 'father_id' 
    has_many :children_of_mother, :class_name => 'Person', :foreign_key => 'mother_id' 
    def children 
    gender == "male" ? children_of_father : children_of_mother 
    end 

Answer 7

我一直在尋找相同的功能，如果你不想返回一個數組而不是ActiveRecord::AssociationRelation，你可以使用<<而不是+。 （See the ActiveRecord documentation）

class Person < ActiveRecord::Base 
    belongs_to :father, :class_name => 'Person' 
    belongs_to :mother, :class_name => 'Person' 

    has_many :children_of_father, :class_name => 'Person', :foreign_key => 'father_id' 
    has_many :children_of_mother, :class_name => 'Person', :foreign_key => 'mother_id' 

    def children 
    children_of_mother << children_of_father 
    end 
end 

Answer 8

我的回答Associations and (multiple) foreign keys in rails (3.2) : how to describe them in the model, and write up migrations是隻爲你！

至於你的代碼，這裏有我的修改

class Person < ActiveRecord::Base 
    belongs_to :father, :class_name => 'Person' 
    belongs_to :mother, :class_name => 'Person' 
    has_many :children, ->(person) { unscope(where: :person_id).where("father_id = ? OR mother_id = ?", person.id, person.id) }, class_name: 'Person' 
end 

所以什麼問題嗎？